A fuel cell generator converts chemical energy directly into electrical energy. Most fuel cell generators comprise a cathode or air electrode and an anode or fuel electrode separated by an electrolyte. At the cathode, oxygen is ionized and the oxide ions migrate through the electrolyte to the anode. At the anode, hydrogen or hydrocarbons react with the oxide ions to form water and release electrons. The released electrons then travel from the anode out of the fuel cell generator through a load and are returned to the cathode, thereby completing the circuit and providing an amount of direct electrical current. It is well known in the art that ion quantities can vary and additional or other constituents can be used.
Fuel cell generators typically comprise a plurality of electrically interconnected fuel cells. The fuel cell generators usually use a hydrogen-bearing and/or carbon-bearing fuel (i.e. natural gas, methane, carbon monoxide) at the anode, and an oxidant (i.e. air, oxygen) at the cathode. A schematic arrangement of one such fuel cell generator, which uses solid oxide fuel cells (SOFC), is described in U.S. Pat. No. 4,395,468.
Because fuel cell generators are efficient, use plentiful and renewable fuels, do not require direct combustion, and produce low undesirable emissions, they are a very attractive energy conversion device. However, although the basic electrochemical processes and schematic arrangement of fuel cell generators are well understood, engineering solutions necessary to lower fabrication costs and make such generators an economical alternative to fossil fuel and other power generation systems remain elusive.
One technical problem with conventional fuel cell generators involves a reformation of the hydrocarbon fuels, which are typically reformed to produce CO, H2, CO2 and H2O as gaseous reformation products. The gaseous reformation products, which are also called reformate, form a suitable fuel gas for the operation of the fuel cell generator to produce electricity.
The process of reformation may be carried out externally or internally (i.e. inside or outside the high-temperature fuel cell module). External reformers, which are known for performing the external reformation process, can be expensive and also take up valuable space in and around the fuel cell generator. One type of fuel reforming SOFC uses pre-reformers and separate stack reformer boards (SRBs) to reform the fuel before reaching the anode. However, the SRBs are expensive and thus it would be preferable to avoid use of SRBs in generators by providing a less expensive alternative.
Prior art arrangements for developing SOFCs having internal fuel reformers may result in excessive cooling of the closed end of the fuel cell due to the fuel reformation, which may decrease performance of the closed end of the fuel cell. Further, excessive cooling of the closed end of the fuel cell may result in high levels of thermal stress on the fuel cell bundles, which may cause damage to the generator.
There is a continuing need for a fuel cell generator construction that addresses thermal stress factors associated with operation of fuel cell bundles, while providing sufficient fuel reformation for the production of electrical energy.